At least some known gas turbine assemblies include a compressor, a combustor, and a turbine. Gas (e.g., ambient air) flows through the compressor, where the gas is compressed before delivery to one or more combustors. In each combustor, the compressed air is combined with fuel and ignited to generate combustion gases. The combustion gases are channeled from each combustor to and through the turbine, thereby driving the turbine, which, in turn, powers an electrical generator coupled to the turbine. The turbine may also drive the compressor by means of a common shaft or rotor.
In some combustors, the generation of combustion gases occurs at two, axially spaced stages. Such combustors are referred to herein as including an “axial fuel staging” (AFS) system, which delivers fuel and an oxidant to one or more downstream fuel injectors. In a combustor with an AFS system, a primary fuel nozzle at an upstream end of the combustor injects fuel and air (or a fuel/air mixture) in an axial direction into a primary combustion zone, and an AFS fuel injector located at a position downstream of the primary fuel nozzle injects fuel and air (or a second fuel/air mixture) in a radial direction into a secondary combustion zone downstream of the primary combustion zone. In some cases, it is desirable to introduce the fuel and air into the secondary combustion zone as a mixture. Therefore, the mixing capability of the AFS injector influences the overall operating efficiency and/or emissions of the gas turbine.